Just in time for cookout season, some unsettling news arrives for guacamole and salsa lovers: Federal testing turned up a wide array of unapproved pesticides on the herb cilantro — to an extent that surprises and concerns government scientists.

At least 34 unapproved pesticides showed up on cilantro samples analyzed by the U.S. Department of Agriculture as part of the agency's routine testing of a rotating selection of produce. Cilantro was the first fresh herb to be tested in the 20-year-old program.

"We are not really sure why the cilantro came up with these residues," said Chris Pappas, a chemist who oversees the Virginia-based USDA pesticide testing. Researchers suspect growers may have confused guidelines for cilantro and flat-leaf parsley, for which more pesticides are approved.

In all, 94 percent of the 184 cilantro samples tested in 2009 came up positive for at least one pesticide, according to an annual Pesticide Data Program report posted online last week.

Chris Campbell, a pesticide analyst for the Environmental Working Group, an advocacy organization, said data show that 44 percent of cilantro samples had residues of at least one pesticide not approved for use on that crop — "higher than I have ever seen" in nearly a decade of analyzing the USDA's pesticide reports.

By comparison, only about 5 percent of spinach samples and 2 percent of apples had at least one pesticide that violated federal rules, according to Campbell's calculations.

The news comes as a one-two punch to cilantro growers and distributors, who in March were hit with a rare "guidance letter" from the Food and Drug Administration citing 28 positive salmonella findings in cilantro since 2004 and warning the industry to "take action to enhance" cilantro safety. This is only the fourth such letter the agency has issued since 2005, according to FDA officials.

Samir Assar, director of produce safety at the FDA, advised consumers with compromised immune systems to consider the salmonella findings when choosing their food. He noted that cooking and thorough washing can reduce, but not necessarily eliminate, the risk from disease-causing bacteria.

Washing did not remove the unapproved pesticides found on cilantro samples tested by USDA.

The cilantro results have captured the attention of both regulators and industry leaders, who said they would take action in response.

"I can assure you that some of these will be followed up," said Ronald Roy, a food safety specialist at the FDA. "When we have a clustering of non-permitted residues around a certain (crop) or with a certain grower, then we investigate to find the cause and correct the specific problem so that it doesn't continue."

"It's something we need to look into," said Kathy Means, vice president of the Produce Marketing Association, a major industry group. "We need to determine: Why this year, why this crop? What's going on? ... There aren't that many cilantro suppliers. And so if you have a problem with one supplier, percentagewise (contamination) may be higher."

Means said that in the wake of the FDA's salmonella letter, the industry had been working on "safety protocols for cilantro" and strategies "to be more careful with cilantro in the future."

Of the samples tested, about 81 percent were grown in the U.S. and 17 percent were imported, with the rest of unknown origin.

Regulatory officials caution that unapproved pesticides on cilantro may not always represent a health threat. Many pesticides not approved for cilantro are OK for use on other plants at certain levels, and regulatory officials recommended taking those levels into consideration when assessing the health threat posed by pesticide residues.

Most levels of the unapproved pesticides found on cilantro did not exceed average limits set by the U.S. Environmental Protection Agency for other crops, the Tribune found. But the fungicide quintozene was found at levels as high as 0.3 parts per million, above the limit of 0.1 ppm set for foods such as tomato paste, and the insecticide diazanon was found at levels as high as 1 ppm, when the limits for other foods on this year's USDA list range from 0.1 to 0.75 ppm.

One insecticide found on 37 percent of the cilantro samples, the organophosphate chlorpyrifros, is approved for cilantro but, in at least one case, was three times higher than the EPA's established limit for the herb.

The USDA's pesticide program usually tests fewer than 20 fresh fruits and vegetables a year from a rotating lineup of produce items. Tested this year were apples, asparagus, cilantro, cucumbers, grapes, green onions, organic lettuce, oranges, pears, potatoes, spinach, strawberries, corn and sweet potatoes — with the vast majority of tests showing no violations of federal rules.

In terms of unapproved pesticide residues, cilantro was the outlier of the group, with at least 34 of 43 pesticide residues not allowed for use on the herb. The next greatest number of non-permissible pesticides were found on cucumbers, with 17.

Azoxystrobin and captan are legal for use on potatoes but were found 16 times at levels that exceeded federal limits, the most such detections in this round of testing. Next on the list for excessive amounts of legal pesticides were imported asparagus and domestic spinach.

Scientists, industry representatives and regulators interviewed for this story say the cilantro test results should be addressed but also note that most Americans — and especially American kids — don't eat piles of cilantro at a sitting.

"We would not pooh-pooh these violations," said Roy, of the FDA. "They all constitute adulterated food. But we are also talking about a relatively minor food. … We have to be risk-based and apply our main resources to foods consumed most often by infants and children — and those are your major fresh fruits and vegetables."

"Cilantro is a very important herb in a lot of cuisines, and it's delicious, and I happen to love it," she said. "So we don't want people thinking that there is anything wrong with cilantro. We need to be sure our food safety protocols are up to snuff and listen to FDA and see what it suggests."

The EPA is concerned by the number of unregistered pesticides found on the crop but believes the small amount of cilantro consumed, paired with relatively low levels of residue, make it unlikely to "present a big risk," said David Miller, chief of the Chemistry and Exposure Branch in the agency's Health Effects Division.

Some medical experts, however, are increasingly concerned about even low-level exposure to pesticides, especially in utero.

"The story of pesticides in food is part of a larger story of our growing knowledge of the exquisite vulnerability of the developing human brain to pesticides and other toxic chemicals," said Dr. Phillip Landrigan, director of the Children's Environmental Health Center at Mount Sinai School of Medicine in New York City. Along with colleagues, he has been researching the effects of chlorpyrifros on humans.

Serving a diet rich in fruits and vegetables remains the healthiest course of action for parents, said Bill Jordan, senior policy adviser to the director of the EPA's pesticide programs.

Jordan suggests thorough washing and peeling to remove some of the surface pesticides on fruits and vegetables like apples, oranges and cucumbers.

"And if people are very, very concerned," he said, "then choosing foods that are grown organically is another option."

Of the six samples of organic cilantro tested by the USDA, only one was found to carry residues of an unapproved pesticide other than the chemical descendants of DDT, which was banned years ago but persists in the environment.

Pappas, of the USDA, advised consumers who are still worried to follow his lead and plant their own.

"I grow cilantro on my deck," he said. "There is less waste because I only take as much as I need, which is only a little at a time, and it's always fresh. If someone is really concerned, they can do that too."